GEOCHRONOLOGY (U-PB/PB-PB) AND ISOTOPIC SIGNATURE (RB-SR/SM-ND) OF THE PALEOPROTEROZOIC GUANAMBI BATHOLITH, SOUTHWEST BAHIA STATE (NE BRAZIL)

Abstract

TThe Guanambi batholith (GB) is located in south-western Bahia, Brazil, where it forms part of the Urandi-Paratinga mobile belt. The batholith extends over an area of almost 6,000 km2 and is mainly composed of syenites and monzonites, with subordinate granites, mafic syenites and lamprophyric dykes. Two main units can be recognized: the multiple intrusions, being divided into four regions (Paratinga, Laguna, Igaporã and Guanambi) and the so-called late-intrusions forming the Cara Suja, Ceraíma and Estreito massifs. U-Pb and Pb-Pb isotopic data demonstrate that the batholith was emplaced 2.05 Ga ago. GB has (i) highly negative initial εNd (-7.4 to -10.6), pointing to an enriched source, and (ii) Sr initial ratios between 0.704 and 0.707. Both chemical and isotopic signatures suggest that GB formed by fractional crystallization of a lamprophyric magma derived from a Paleoproterozoic enriched mantle source.